The Rocky Mountain Multiple Sclerosis Center is one of a few centers devoted solely to the care if patients with multiple sclerosis, and is the only center of its type in the State of Colorado. Using records from the Center, the local chapter of the National Multiple Sclerosis Society, hospital records, and physician records we estimated the prevalence of multiple sclerosis for Weld and Larimer Counties, after accounting for duplicate cases. Crude point prevalence for the two-county region was 84 per 100,000. Methodological results revealed that the highest yield sources of cases were the MS service organizations and the neurology practice chart reviews. Prevalence surveys which neglect these sources may underestimate MS prevalence by as much as 20% to 40%. A manuscript "Higher than expected prevalence of multiple sclerosis in Northern Colorado: Dependence on methodologic issues," has been submitted for publication.